JPH094492A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the increase of NOx discharge quantity immediately after switching the mode from lean to stoichiometric air in a system, which is provided with the lean NOx catalyst and the three dimensional catalyst in the downstream of the lean NOx catalyst in an exhaust system thereof. SOLUTION: A timer TMS is cleared at the time of switching the mode from lean to stoichiometric air (S16), and the timer TMS is counted up during the time when the stoichiometric air mode is continued (S17) so as to measure the passing time TMS after switching the mode from lean to the stoichiometric air. The injection finishing time is set on the basis of the engine operating condition (S22), and the correction quantity is computed in response to the passing time TMS after switching the mode from lean to the stoichiometric air (S23) so as to correct the injection finishing time (S24). Discharge quantity of HC from the engine immediately after switching the mode from lean to the stoichiometric air is increased by correcting the injection finishing time or correcting the ignition time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine control device in which the air-fuel ratio of an air-fuel mixture supplied to an engine is switched between a stoichiometric air-fuel ratio and a lean air-fuel ratio according to operating conditions.

[0002]

2. Description of the Related Art Conventionally, for the purpose of improving fuel efficiency, the air-fuel ratio of an air-fuel mixture supplied to an engine is set to a stoichiometric air-fuel ratio (hereinafter also referred to as "stoichiometric"; A / F = 14.6) under predetermined operating conditions.
Has proposed a lean control engine in which a lean air-fuel ratio (for example, A / F = 20 to 22) is switched (see Japanese Patent Laid-Open No. 3-217640).

Further, in such a lean control engine, a so-called lean NOx catalyst is provided in the exhaust system in order to reduce the NOx emission amount during operation at a lean air-fuel ratio. This uses zeolite as a base material of the catalyst, adsorbs HC on the zeolite during operation at a stoichiometric air-fuel ratio, and reduces NOx by the adsorbed HC and HC discharged from the engine during operation at a lean air-fuel ratio. Is.

A three-way catalyst is provided downstream of the lean NOx catalyst for purification of exhaust gas during operation at the stoichiometric air-fuel ratio.

[0005]

However, in such a conventional lean control engine, when the lean air-fuel ratio is changed to the stoichiometric air-fuel ratio, it is considered that HC is adsorbed by the zeolite of the lean NOx catalyst. Therefore, until the adsorption limit is reached, the exhaust air-fuel ratio at the three-way catalyst inlet becomes lean (NOx cannot be reduced due to lack of HC), and the NOx emission amount at the three-way catalyst outlet increases. There was a point.

When the amount of HC adsorbed in the lean NOx catalyst is saturated, the exhaust air-fuel ratio at the three-way catalyst inlet is not made lean, and the NOx emission amount returns to the original value. The present invention has been made in view of such conventional problems, and an object thereof is to be able to suppress an increase in the NOx emission amount immediately after switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio.

[0007]

According to the present invention, air-fuel ratio switching means for switching the air-fuel ratio of the air-fuel mixture supplied to the engine between the stoichiometric air-fuel ratio and the lean air-fuel ratio according to operating conditions is provided, while the exhaust system is theoretically equipped. An engine equipped with a lean NOx catalyst that adsorbs HC during operation at an air-fuel ratio, and reduces NOx by the adsorbed HC and HC exhausted from the engine during operation at a lean air-fuel ratio, and further includes a three-way catalyst downstream thereof Is assumed.

According to the first aspect of the present invention, as shown in FIG. 1, the combustion state of the engine is controlled so that the HC emission amount from the engine increases immediately after switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio. By providing means (combustion state control means),
It constitutes an engine control device. That is, immediately after switching from the lean air-fuel ratio (lean) to the stoichiometric air-fuel ratio (stoichiometric), HC is adsorbed by the lean NOx catalyst, but at this time, the combustion state of the engine is controlled and H from the engine is controlled.
Increase C emission. Therefore, since more HC is exhausted than being adsorbed by the lean NOx catalyst, the exhaust air-fuel ratio at the three-way catalyst inlet is set to a stoichiometric state (in other words, NOx is reduced by the increased HC), and the three-way It is possible to reduce the NOx emission amount at the catalyst outlet.

According to the second aspect of the present invention, immediately after switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio, the HC emission amount from the engine increases, and the HC emission amount gradually decreases with the lapse of time so that the engine emission amount is gradually reduced. A means for controlling the combustion state (combustion state control means) is provided to configure an engine control device. That is, immediately after switching from lean to stoichiometric, after increasing the HC emission amount from the engine, the HC emission amount is gradually decreased with the passage of time. Therefore, as the lean NOx catalyst approaches the HC adsorption limit, the HC adsorption amount decreases. It can respond to changes in quantity.

The invention according to claim 3 is characterized in that correction time setting means for setting a correction time for increasing the HC emission amount by the combustion state control means is set by the engine speed and the load (see FIG. 1). . That is, by setting the correction time for increasing the HC emission amount according to the engine speed and the load, the desired HC can be maintained until the lean NOx catalyst approaches the HC adsorption limit regardless of the difference in the HC emission amount due to the engine speed and the load. Emissions can be obtained.

The invention according to claim 4 is characterized in that correction amount setting means for setting the correction amount in the HC emission increasing direction by the combustion state control means according to the engine speed and the load is provided (FIG. 1). reference). That is, by setting the correction amount in the direction of increasing the HC emission amount depending on the engine speed and the load, the desired amount can be set in the low speed low load to the high speed high load regardless of the difference in the HC discharge amount due to the engine speed and the load. It is possible to obtain the HC emission amount of.

According to the fifth aspect of the present invention, the stability detecting means for detecting the stability of the engine and the correction amount for varying the HC emission amount increasing direction by the combustion state control means according to the stability of the engine are corrected. It is characterized in that a quantity varying means is provided (see FIG. 1). That is, by varying the correction amount in the direction of increasing the HC emission amount according to the stability of the engine, it is possible to purify exhaust gas to the stability limit while preventing deterioration of the stability of the engine due to overcorrection. Becomes

The invention according to claim 6 is characterized in that the combustion state control means controls the fuel injection timing to the engine. That is, the HC injection amount is controlled by controlling the fuel injection timing to the engine, and the HC emission amount is surely increased by delaying the fuel injection timing (particularly the injection end timing) from the proper timing. Can be made.

According to a seventh aspect of the present invention, the combustion state control means controls the ignition timing of the engine. That is, the HC emission amount is controlled by controlling the ignition timing to the engine, and the HC emission amount can be reliably increased by advancing the ignition timing from an appropriate timing, for example.

[0015]

Embodiments of the present invention will be described below. First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows the system configuration. Engine 1
Air is sucked into the combustion chamber of each cylinder from the air cleaner 2 through the throttle valve 3 and the intake manifold 4. Each branch of the intake manifold 4 is provided with an electromagnetic fuel injection valve 5.
A fuel-air mixture is generated by the fuel injected from the fuel cell. Then, the air-fuel mixture is ignited by the ignition plug 6 in the combustion chamber and burns.

The fuel injection valve 5 is opened by being energized by a drive pulse signal output from a control unit 12 which will be described later at a timing synchronized with the rotation of the engine, and injects fuel adjusted to a predetermined pressure. Therefore, the fuel injection amount is controlled by the pulse width of the drive pulse signal. Exhaust gas from the engine 1 passes through an exhaust manifold 7 and an exhaust pipe 8
Leading to.

In the middle of the exhaust pipe 8, a lean NOx catalyst 9 and a three-way catalyst 10 are provided separately in the same container on the upstream side and the downstream side. Lean NOx catalyst 9
Uses zeolite as the base material of the catalyst, adsorbs HC on the zeolite during stoichiometric operation, and absorbs HC by the adsorbed HC and HC discharged from the engine during lean operation.
Ox is reduced, and the NOx reduction function makes it possible to suppress the NOx emission amount even during lean combustion in which a large amount of oxygen exists in the exhaust gas.

The three-way catalyst 10 is
It has the function of oxidizing HC and CO and reducing NOx. Then, the exhaust gas passes through the catalysts 9 and 10 and is then discharged through the muffler 11. The control unit 12 for controlling the operation of the fuel injection valve 5 has a built-in microcomputer and receives signals from various sensors.

The various sensors are throttle valves.
3 which detects the intake air flow rate Q of the engine 1 on the upstream side of
Afflow meter 13, engine 1 camshaft rotation
Indirectly outputs the rank angle signal and unit crank angle signal
Crank angle sensor 14 that can detect engine speed N
Check the cooling water temperature Tw in the water jacket of engine 1.
Attached to water temperature sensor 15 and exhaust manifold 7
Exhaust related to the air-fuel ratio of the air-fuel mixture drawn into the engine 1
O that outputs a voltage signal corresponding to the oxygen concentration in the air ₂Sensor
16 mag is provided.

Here, the control unit 12
Controls the operation of the fuel injection valve 5 by performing arithmetic processing based on signals from the various sensors as described below. Next, the contents of arithmetic processing of the control unit 12 will be described with reference to the flowcharts of FIGS. It should be noted that this flow is executed every predetermined time Δt (for example, 10 ms).

In step 1 (denoted as S1 in the drawing; the same applies hereinafter), the intake air flow rate Q is detected based on the signal from the air flow meter 13. In step 2, the engine speed N is detected based on the signal from the crank angle sensor 14. In Step 3, from the intake air flow rate Q and the engine speed N, the basic fuel injection amount (basic injection pulse width) Tp = K × Q / N (K which corresponds to stoichiometry (A / F = 14.6)
Is a constant).

In step 4, the cooling water temperature Tw is detected based on the signal from the water temperature sensor 15. In step 5, the water temperature increase correction coefficient Ktw for increasing the fuel amount at low temperature is set by referring to the map based on the cooling water temperature Tw. In step 6, it is determined whether or not the cooling water temperature Tw is, for example, 60 ° C. or higher. When the temperature is lower than 60 ° C., open control is performed to set the air-fuel ratio to about stoichiometry, so the process proceeds to step 7.

In step 7, the basic fuel injection amount Tp and
From the water temperature increase correction coefficient Ktw and the voltage correction amount (ineffective injection pulse width) Ts set based on the battery voltage, the open control fuel injection amount (pulse width) T is calculated according to the following equation.
Calculate i. Ti = Tp × (1 + Ktw) + Ts When the cooling water temperature Tw is 60 ° C. or higher, the process proceeds to step 8 in order to realize the air-fuel ratio switching control according to the operating region.

In step 8, the target air-fuel ratio T is set for each operating region of the engine speed N and the basic fuel injection amount (load) Tp.
Referring to the map shown in FIG. 5 which defines AF, the actual N, T
The target air-fuel ratio TAF is obtained from p by searching. Incidentally, FIG.
Then, the lean region of the target air-fuel ratio TAF = 20 to 22 is covered by the stoichiometric region of the target air-fuel ratio TAF = 14.6, and this stoichiometric region is the rich region of the target air-fuel ratio TAF = 12 (output mixture ratio region). Is around.

At step 9, the target air-fuel ratio TAF> 15
It is determined whether or not (lean air-fuel ratio), and if YES (lean air-fuel ratio), after lean flag FL = 1 is set in step 10, the process proceeds to step 13 for calculation of the fuel injection amount Ti. If the determination in step 9 is no, the process proceeds to step 11. In step 11, it is determined whether or not the target air-fuel ratio TAF <14.5 (rich air-fuel ratio). If YES (rich air-fuel ratio), after the lean flag FL = 0 is set in step 12,
To calculate the fuel injection amount Ti, the process proceeds to step 13.

In step 13, the basic fuel injection amount Tp is corrected to correspond to the target air-fuel ratio TAF and the open control fuel injection amount Ti is calculated as in the following equation. Ti = Tp × (14.6 / TAF) × (1 + Ktw) + Ts If the determination in step 11 is NO, the target air-fuel ratio TAF
= 14.6 (stoichi), the process proceeds to step 14.

In step 14, the value of the lean flag FL (FL = 0 during stoichiometric operation or rich operation, FL = 1 during lean operation) is determined. When FL = 1, it means that the lean-to-stoichi switching command is issued during the lean operation now. At this time, the routine proceeds to step 15, where the lean flag F is entered.
Set L = 0. Further, in the next step 16, the timer TMS for measuring the elapsed time after the lean-to-stoichi switching is cleared (TMS = 0).

When FL = 0, the stoichiometric operation is continuing, and so on, the routine proceeds to step 17, where the timer TMS is counted up by the execution time interval Δt of this routine (TMS).
= TMS + At). Further, in the next step 18, the value of the timer TMS is compared with a predetermined maximum value MAX, and TMS is compared.
If> MAX, step 19 regulates TMS = MAX.

After this, the routine proceeds to step 20, where the air-fuel ratio feedback correction coefficient α is calculated based on the signal from the O ₂ sensor 16. Specifically, the O ₂ sensor output voltage VO
₂ is compared with the predetermined slice level SL, and VO ₂ > SL
In the case of (rich), the air-fuel ratio feedback correction coefficient α
Is decreased by Δα (α = α-Δα), and when VO ₂ <SL (lean), the air-fuel ratio feedback correction coefficient α is changed by Δα.
Increase (α = α + Δα).

In the next step 21, the basic fuel injection amount Tp corresponding to stoichiometry is used and corrected by the air-fuel ratio feedback correction coefficient α and the fuel injection amount Ti for closed control is calculated as in the following equation. Ti = Tp × (1 + Ktw) × α + Ts After the calculation of the fuel injection amount Ti (step 7, step 13 or step 21), the process proceeds to steps 22 to 25.

In step 22, the map shown in FIG. 6 in which the injection end timing (crank angle before intake bottom dead center) is determined for each operating region of the engine speed N and the basic fuel injection amount (load) Tp, The injection end timing is obtained by searching from the actual N and Tp. In step 23, the correction amount (retard correction amount) of the injection end timing is calculated based on the value of the timer TMS indicating the elapsed time after the lean-to-stoichi switching. This correction amount is maximum immediately after switching (near TMS = 0), and gradually decreases as time passes, and MAX time elapses (TMS = MA).
X) so that it becomes 0. In other words, the correction amount is
It is calculated in proportion to MAX-TMS.

In step 24, the injection end timing (basic injection end timing) obtained from N and Tp in step 22 is set.
Compensate to the retard side by the amount of compensation calculated in 23. When the injection end timing is represented by the crank angle before the intake bottom dead center, the correction amount may be subtracted. In step 25, the injection start timing before the time corresponding to the fuel injection amount (pulse width) Ti is calculated from the corrected injection end timing.

As a result, at the calculated injection start timing, a drive pulse signal having a pulse width of Ti is output to the fuel injection valve 5 and fuel injection is performed. In this embodiment,
The steps 6 to 21 correspond to the air-fuel ratio switching means, and the steps 23 and 24 correspond to the combustion state control means. Next, the operation of this embodiment will be described.

In this embodiment, the fuel injection timing (particularly the injection end timing) is retarded immediately after switching from lean to stoichiometric, and the retard amount is gradually decreased with the lapse of time. FIG. 7 shows the relationship between the injection end timing and the amount of HC emission from the engine. The injection end timing is usually set before the intake bottom dead center, but as can be seen from FIG. 7, the HC emission amount increases as the injection end timing approaches the intake bottom dead center.

Therefore, as shown in FIG. 8, immediately after the change from lean to stoichiometric, the injection end timing is retarded to near the suction bottom dead center, and the retard amount is gradually reduced with the passage of time to obtain the original value. By returning to the characteristic of FIG. 6, the amount of HC emission from the engine can be increased by the amount of the retard correction. Next, H from the engine immediately after switching from lean to stoichiometric
The effect of increasing the amount of C emission will be described with reference to FIG.

A is the inlet of the lean NOx catalyst, B is the inlet of the three-way catalyst (exit of the lean NOx catalyst), and C is the outlet of the three-way catalyst. In the conventional example, when the air-fuel ratio is switched from lean to stoichiometric at time t ₀ , the exhaust air-fuel ratio at point A changes stepwise, but the HC emission amount from the engine does not change in stoichiometric / lean, HC at point A does not change.

On the other hand, HC at point B is smaller than point A due to the oxidation performance of the lean NOx catalyst even during lean operation, but when the air-fuel ratio is switched to stoichiometric at time t ₀ , H at point B is reached.
C temporarily decreases. This is a part of HC is lean NO
This is because it is adsorbed by the zeolite of the x catalyst. For this reason, the exhaust air-fuel ratio at the points B and C does not immediately reach the stoichiometric state, and the change is delayed. As a result, N
Ox reduction action is not exhibited, and NOx at point C temporarily increases.

On the other hand, in the present invention (this embodiment), when the air-fuel ratio is switched from lean to stoichiometric at time t ₀ ,
At the same time, by retarding the injection end timing, the amount of HC discharged from the engine is increased and the HC at point A is increased. Therefore, even if a part of the HC is adsorbed by the zeolite of the lean NOx catalyst, it is possible to suppress the decrease of the HC at the point B. As a result, the exhaust air-fuel ratios at points B and C are immediately stoichiometric, so NOx at point C does not increase.

For this reason, it is possible to suppress an increase in the NOx emission amount when switching from lean to stoichiometric. Next, a second embodiment of the present invention will be described with reference to FIGS. FIG.
Is a flowchart of the second embodiment. However, this figure
The flowchart of 10 is executed in place of that of FIG. 4 following the flowchart of FIG. 3 of the first embodiment.

In the second embodiment, immediately after switching from lean to stoichiometric, not the fuel injection timing but the ignition timing is corrected to increase the HC emission amount from the engine. Therefore, the difference from the flowchart of FIG. 4 is only the process after the calculation of the fuel injection amount Ti, and the process starting from step 22 will be described.

In step 22, referring to the map shown in FIG. 6, in which the injection end timing (crank angle before intake bottom dead center) is determined for each operating region of the engine speed N and the basic fuel injection amount (load) Tp, The injection end timing is obtained by searching from the actual N and Tp. In step 25, the injection start timing before the time corresponding to the fuel injection amount (pulse width) Ti is calculated from the obtained injection end timing. As a result, at the calculated injection start timing, a drive pulse signal having a Ti pulse width is output to the fuel injection valve 5 and fuel injection is performed.

At step 26, referring to the map shown in FIG. 11, in which the ignition timing (crank angle before compression top dead center) is determined for each operating region of the engine speed N and the basic fuel injection amount (load) Tp, The ignition timing is obtained by searching from N and Tp. In step 27, the ignition timing correction amount (advance correction amount) is calculated based on the value of the timer TMS indicating the elapsed time after the lean-to-stoichi switching. This correction amount is maximum immediately after switching (near TMS = 0), gradually decreases with the passage of time, and becomes 0 after the passage of MAX time (TMS = MAX). In other words, the correction amount is MAX-TM.
It is calculated in proportion to S.

At step 28, the ignition timing (basic ignition timing) obtained from N and Tp at step 26 is corrected to the advance side by the correction amount obtained at step 27. When the ignition timing is represented by the crank angle before the compression top dead center, the correction amount may be added. As a result, at the corrected ignition timing, an ignition signal is output to an ignition coil (not shown), and the ignition plug 6 is ignited.

In this embodiment, the steps 6 to 21 correspond to the air-fuel ratio switching means, and the steps 27 and 28 correspond to the combustion state control means. Next, the operation of this embodiment will be described. In the present embodiment, the ignition timing is advanced immediately after switching from lean to stoichiometric, and the advance amount is gradually decreased with the passage of time.

FIG. 12 shows the ignition timing and the HC from the engine.
It shows the relationship with the amount of emissions. As you can see from Figure 12,
As the ignition timing is advanced, the HC emission amount increases. Therefore, as shown in FIG. 13, immediately after switching from lean to stoichiometric, the ignition timing is advanced, and the advance amount is gradually reduced with the passage of time, so that the original characteristics of FIG. 11 are restored. The amount of HC emission from the engine can be increased by the amount of advance angle correction.

By increasing the HC emission amount from the engine immediately after the lean-to-stoichi switching, it is possible to suppress the increase in the NOx emission amount at the three-way catalyst outlet, as in the first embodiment. In addition, by combining the first embodiment and the second embodiment, immediately after switching from lean to stoichiometric, both the fuel injection timing and the ignition timing are corrected to increase the HC emission amount from the engine. You may

Next, a third embodiment of the present invention will be described with reference to FIGS. 14 to 15 are flowcharts of the third embodiment. However, the flowcharts of FIGS. 14 to 15 follow the flowchart of FIG. 3 of the first embodiment, and
Be executed on behalf of. The difference from the flowchart of FIG. 4 is that after the processing of steps 15 and 16 when a lean-to-stoichi switching command is issued, the processing of step 30 and the calculation of the fuel injection amount Ti (step 21) are performed. The processing after step 31 (FIG. 15).

In step 30, when a lean-to-stoichi switching command is issued, a correction time (delay angle time) for the injection end timing is determined for each operating region of the engine speed N and the basic fuel injection amount (load) Tp. Refer to the map shown in Figure 16,
The correction time is obtained by searching from the actual N and Tp. Here, the correction time is set shorter as the load increases at high speed.
This correction time is the time until the lean NOx catalyst reaches the HC adsorption limit, and this time is basically the HC in the exhaust gas.
This is because the amount of the exhaust gas is determined by the amount of the exhaust gas, and the larger the exhaust amount, the more the amount of HC.

Next, step 31 and thereafter (FIG. 15), which is the process after the calculation of the fuel injection amount Ti, will be described. Step 31
Then, the engine speed N and the basic fuel injection amount (load) Tp
By referring to the map shown in FIG. 6 in which the injection end timing (crank angle before the intake bottom dead center) is determined for each operation region, the injection end timing is obtained from the actual N, Tp.

In step 32, the value of the timer TMS indicating the elapsed time after the lean-to-stoichi switching is compared with the correction time calculated in step 30. If TMS≤correction time, the correction time immediately after the lean-to-stoichi switching is set. Therefore, steps 33 and 34 are executed. In addition, including lean operation
TMS = MA if not immediately after switching from lean to stoichiometric
Since it is X, TMS> correction time, and the process proceeds to step 35 without executing steps 33 and 34.

In step 33, referring to the map shown in FIG. 17 in which the correction amount (retardation amount) of the injection end timing is determined for each operating region of the engine speed N and the basic fuel injection amount (load) Tp, the actual The correction amount is obtained by searching from N and Tp. Here, the correction amount (retardation amount) is set larger as the load becomes higher at high speeds, and set smaller as the load becomes lower at low speeds. This is because it is not desirable to make the combustion state worse in the low-speed low-load region than in the high-speed high-load region. Because there is no. The correction amount (retard angle amount) is determined by the characteristics of the engine.
It is about 60 ° CA. .

The correction amount obtained here may be used as an initial correction amount, and the correction amount may be decreased with time. In step 34, the injection end timing (basic injection end timing) obtained from N and Tp in step 31 is corrected to the retard side by the correction amount obtained in step 33. When the injection end timing is represented by the crank angle before the intake bottom dead center, the correction amount may be subtracted.

In step 35, the injection start timing before the time corresponding to the fuel injection amount (pulse width) Ti from the corrected injection end timing is calculated. As a result, at the calculated injection start timing, a drive pulse signal having a Ti pulse width is output to the fuel injection valve 5 and fuel injection is performed. In this embodiment, the steps 6 to 21 correspond to the air-fuel ratio switching means, and the steps 32 to 34 correspond to the combustion state control means. Further, the part of step 30 corresponds to the correction time setting means, and the part of step 33 corresponds to the correction amount setting means.

According to this embodiment, since the correction time and the correction amount are determined based on the engine speed and the load, the lean NOx catalyst reaches the HC adsorption limit regardless of the difference in the HC emission amount depending on the engine speed and the load. Until approaching, a desired amount of HC emission can be obtained in a low speed low load to a high speed high load. Next, a fourth embodiment of the present invention will be described with reference to FIG.

FIG. 18 is a flow chart of the fourth embodiment. However, the flowchart of FIG. 18 is executed instead of FIG. 15 following the flowchart of FIG. 14 of the third embodiment. The difference from the third embodiment is that the fuel injection amount Ti
Is only the process after the calculation of
The following will be described.

In step 41, referring to the map shown in FIG. 6, in which the injection end timing (crank angle before intake bottom dead center) is determined for each operating region of the engine speed N and the basic fuel injection amount (load) Tp, The injection end timing is obtained by searching from the actual N and Tp. In step 42, the value of the timer TMS indicating the elapsed time after lean-to-stoichi switching is compared with the correction time calculated in step 30, and if TMS ≦ correction time,
Since it is within the correction time immediately after the switching from lean to stoichiometric, steps 43 to 49 are executed.

When the lean-to-stoichi switching is not performed immediately, including during lean operation, TMS = MAX, so TMS> correction time is reached, and steps 43 to 49 are not executed, and the process proceeds to step 50. . In step 43, the same map as that of FIG. 17 in which the basic correction amount (basic retardation amount) R ₀ of the injection end timing is determined for each operation region of the engine speed N and the basic fuel injection amount (load) Tp, The basic correction amount R ₀ is obtained by searching from the actual N and Tp. Here, the basic correction amount R ₀ is set to be larger as the speed and load become higher.

At step 44, the stability of the engine is detected. Specifically, the engine speed N (cycle of the reference crank angle signal) in the combustion stroke of each cylinder is continuously detected, and the amount of rotation fluctuation (standard deviation, variance, etc.) is calculated,
The stability is detected based on this. In step 45, the detected stability is compared with a predetermined value. If stability ≧ predetermined value (stable state), the routine proceeds to step 46, where the increment ΔR is increased to increase the correction amount (plus side). ). If stability <predetermined value (unstable state), step
Proceeding to 47, the increment ΔR is decreased to decrease the correction amount (minus side).

At step 48, the basic correction amount R ₀ is incremented by Δ.
R is added to calculate the correction amount R = R ₀ + ΔR. In step 49, the injection end timing (basic injection end timing) obtained from N and Tp in step 41 is corrected to the retard side by the correction amount R obtained in step 48. When the injection end timing is represented by the crank angle before the intake bottom dead center, the correction amount R may be subtracted.

In step 50, the injection start timing before the time corresponding to the fuel injection amount (pulse width) Ti from the corrected injection end timing is calculated. As a result, at the calculated injection start timing, a drive pulse signal having a Ti pulse width is output to the fuel injection valve 5 and fuel injection is performed. In this embodiment, steps 6 to 21 correspond to air-fuel ratio switching means, and steps 42 to 49 correspond to combustion state control means. The step 30 corresponds to the correction time setting means, the step 43 corresponds to the correction amount setting means, the step 44 corresponds to the stability detecting means, and the steps 45 to 45
The portion 48 corresponds to the correction amount varying means.

According to the present embodiment, the injection end timing can be retarded to the engine stability limit, so that the H level required for exhaust gas purification can be increased.
It is possible to secure a sufficient amount of C emission. Further, there is a possibility that the relationship between the fuel injection timing and the engine stability may change due to the change of the engine with time, for example, the change of the fuel intake characteristic due to the deposit adhered to the intake valve.

In the third and fourth embodiments, the fuel injection timing is corrected (retarded) in order to increase the amount of HC discharged from the engine. However, in these embodiments as well, As in the second embodiment, the ignition timing may be corrected (advanced) to increase the amount of HC discharged from the engine. Further, in the first to fourth embodiments, the amount of HC emissions from the engine is increased immediately after switching from lean to stoichiometric. However, even after switching from lean to rich, the amount of HC emission from the engine is increased. HC
The discharge amount may be increased.

[0063]

As described above, according to the first aspect of the present invention, immediately after switching from lean to stoichiometric, even if HC is adsorbed on the lean NOx catalyst, the exhaust air-fuel ratio at the three-way catalyst inlet is increased. Is brought to a stoichiometric state to reduce the NOx emission amount at the outlet of the three-way catalyst.

According to the second aspect of the present invention, immediately after switching from lean to stoichiometric, the HC emission amount from the engine is increased, and then the HC emission amount is gradually decreased with the passage of time. It is possible to obtain the effect that the control becomes corresponding to the change of. According to the third aspect of the present invention, it is possible to obtain the desired HC emission amount until the lean NOx catalyst approaches the HC adsorption limit regardless of the difference in the HC emission amount depending on the engine speed and the load. To be

According to the fourth aspect of the present invention, the desired HC emission amount can be obtained in the low speed low load to high speed high load range regardless of the difference in the HC emission amount depending on the engine speed and the load. The effect is obtained. According to the invention of claim 5, the correction amount in the increasing direction of the HC emission amount is changed according to the stability of the engine. Therefore, deterioration of the stability of the engine due to overcorrection is prevented, and the stability limit is reached. There is an effect that exhaust gas can be purified and it is possible to cope with a change over time.

According to the invention of claim 6, the fuel injection timing to the engine is controlled so that the required HC from the engine can be obtained.
The effect that the emission amount can be reliably increased is obtained. According to the invention of claim 7, there is an effect that the ignition timing to the engine can be controlled to surely increase the required HC emission amount from the engine.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention.

FIG. 2 is a system configuration diagram of the first embodiment.

FIG. 3 is a flowchart of the first embodiment (part 1).

FIG. 4 is a flowchart of the first embodiment (part 2).

FIG. 5 is a diagram showing a map for setting a target air-fuel ratio.

FIG. 6 is a diagram showing a map for setting the injection end timing.

FIG. 7 is a diagram showing a relationship between an injection end timing and an HC emission amount.

FIG. 8 is a diagram showing an operation at the time of switching from lean to stoichiometric.

FIG. 9 is a diagram showing a NOx emission reduction effect.

FIG. 10 is a flowchart of the second embodiment.

FIG. 11 is a diagram showing an ignition timing setting map.

FIG. 12 is a diagram showing a relationship between ignition timing and HC emission amount.

FIG. 13 is a diagram showing an operation when switching from lean to stoichiometric.

FIG. 14 is a flowchart of the third embodiment.

FIG. 15 is a flowchart of the third embodiment.

FIG. 16 is a diagram showing a correction time setting map.

FIG. 17 is a diagram showing a correction amount setting map.

FIG. 18 is a flowchart of the fourth embodiment.

[Explanation of symbols]

1 Engine 5 Fuel Injection Valve 9 Lean NOx Catalyst 10 Three-Way Catalyst 12 Control Unit 13 Air Flow Meter 14 Crank Angle Sensor 15 Water Temperature Sensor 16 O ₂ Sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location F02D 43/00 ZAB F02D 43/00 ZAB 301 301J 301B F02P 5/15 ZAB F02P 5/15 ZABK

Claims (7)

[Claims] 1. An air-fuel ratio switching means for switching the air-fuel ratio of an air-fuel mixture supplied to an engine between a stoichiometric air-fuel ratio and a lean air-fuel ratio in accordance with operating conditions, while the exhaust system is provided with HC during operation at the stoichiometric air-fuel ratio. NOx is generated by the adsorbed HC and the HC discharged from the engine during operation at a lean air-fuel ratio.
In a engine equipped with a lean NOx catalyst that reduces the amount of CO, and a three-way catalyst further downstream thereof, the combustion of the engine is increased so that the HC emission amount from the engine increases immediately after switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio. An engine control device comprising means for controlling a state. 2. An air-fuel ratio switching means for switching the air-fuel ratio of the air-fuel mixture supplied to the engine between a stoichiometric air-fuel ratio and a lean air-fuel ratio in accordance with operating conditions, while the exhaust system supplies HC during operation at the stoichiometric air-fuel ratio. NOx is generated by the adsorbed HC and the HC discharged from the engine during operation at a lean air-fuel ratio.
In an engine equipped with a lean NOx catalyst that reduces CO2 and a three-way catalyst on the downstream side of the engine, the HC emission from the engine increases immediately after switching from the lean air-fuel ratio to the stoichiometric air-fuel ratio, and the HC emission increases with time. An engine control device comprising means for controlling the combustion state of the engine so that the amount gradually decreases. 3. A correction time setting means for setting the correction time for increasing the HC emission amount by the means for controlling the combustion state of the engine according to the engine speed and the load. The engine control device described. 4. A correction amount setting means for setting a correction amount for increasing the HC emission amount by the means for controlling the combustion state of the engine according to the engine speed and the load. Item 4. The engine control device according to any one of items 3. 5. A stability detecting means for detecting the stability of the engine and a means for controlling the combustion state of the engine.
The engine control according to any one of claims 1 to 4, further comprising: a correction amount varying unit that varies a correction amount in the C emission increasing direction according to the stability of the engine. apparatus. 6. The engine according to claim 1, wherein the means for controlling a combustion state of the engine controls a fuel injection timing to the engine. Control device. 7. The engine control according to any one of claims 1 to 5, wherein the means for controlling the combustion state of the engine controls the ignition timing of the engine. apparatus.